1. Field of the Invention
This invention relates to a method for the debarking of logs.
2. Description of the Related Art
In the production of chemical and/or groundwood pulp from logs, the fibre yield from the bark of the logs is often small and of low quality. In addition, the presence of the bark in the pulp causes problems relating to the use of extractives and an increased consumption of chemicals. Accordingly, the logs are usually debarked prior to defibration. The need for debarking depends primarily upon the intended product, but also on the equipment and process used for defibration. For instance, the process used for the production of bleached softwood sulphate tolerates the presence of small quantities of bark, whereas the production of groundwood pulp generally requires complete debarking of the logs.
Presently, drum debarkers are typically used for the debarking of pulpwood. However, other debarking methods include the use of cambio debarkers, rotor debarkers of high-pressure water jets.
Trees have a cambium layer between the bark and the wood. It is the cambium layer that is the living and continuously growing part of the tree. The cells in this layer divide continuously, which is why they tend to have a lower mechanical strength than cells elsewhere in the tree. In debarking, the aim is to remove the bark together with the cambium layer. Characteristically, the cambium comprises a high pectin content. Pectin polymers consist of galacturonic acid, ramnose, arabinose and galactose. As well, the cambium comprises hemicellulose, cellulose and protein.
A significant disadvantage of current mechanical debarking methods and equipment is that in order to achieve a desired degree of debarking it is necessary to continue the debarking process well beyond the time it takes to remove substantially all the bark, in order that pieces which hold steadfastly to the logs can be removed. This results in significant wood loss especially in the trunk areas already completely debarked. Moreover, it leads to increased debarking times and greater energy consumption.